Idea: instead of just strait up mining an entire asteroid the mining capital could pick up and move an asteroid between systems. This would prevent other ships from becoming obsolete as it could have sub-par mining ability. Additionally, such a ship would provide diminishing returns. And, I estimate the value of moving a low-sec asteroid to high-sec will be balanced by the chance of losing you capital each trip, even more so if the align time is proportional to its size. If even align time is not enough to balance it, you could limit the size of asteroids it could take requiring mining ships to first mine asteroids down to the correct size before they could be moved.